1. Field of the Invention
The present invention relates to a tapping machine which carries out a tapping process in a previously drilled hole in a workpiece, such as a piece of sheet metal, and more specifically, relates to a tapping machine by which the tapping process on the workpiece is caried out automatically, under numerical control, by means of a tapping head after moving and positioning the workpiece.
2. Description of the Present Art
In general, in a tapping machine, the tapping process is carried out on a plurality of holes which have been drilled previously in a workpiece, such as a piece of sheet metal, using a drill press or a punch press. Conventionally, the number of holes which are tapped is exceedingly small in comparison to the number of holes drilled in advance in the workpiece, so that the positioning of the workpiece relative to the tapping machine is performed manually. For this reason, the work efficiency is poor, so that the interest is now toward positioning the workpiece automatically. However, in the case of multi-variety, small volume production, the program for positioning the workpiece automatically must be drawn up in order to be compatible with the workpiece each time the type or workpiece is changed , so that drawing up these programs becomes a problem.
In addition, in a conventional tapping machine, the spindle of the tapping machine generally rotates in a suitable manner and the advancement of the spindle is forced by means of a lead screw which conforms to the tapping pitch. Accordingly, in the case where the machining capacity of the tap decreases as a result of tap wear, the problem occurs in which the tap is forcibly advanced causing breakage.